For a few years self-etching adhesives have been known in the field of dentistry. They combine an etching and bonding step so that the surface is prepared for the polymer or composite filling. They are as a rule two-component materials which must be either mixed directly before their application or applied sequentially. One of the first single-component, single-flask adhesives in which no mixing or sequential application of two components is required came onto the market with iBOND™ Gluma Inside (Heraeus Kulzer). It can be considered as a disadvantage that iBOND™ Gluma Inside must be stored cold (4-10° C.) since there is the possibility that due to a hydrolysis of the components during storage at higher temperatures a short-term polymerization will occur in the packaging.
Various hydrolysis-stable monomers for dental materials have already been proposed, among them sulfonic acid derivatives with (WO03070198A1, US20030187094A1) and without siloxane groups (US20030055124A1) as well as acrylester phosphonic acids and their esters (U.S. Pat. No. 6,710,149B2, DE10206451A1, U.S. Pat. No. 6,172,131B1, U.S. Pat. No. 6,812,266B2) WO03035013A1), or carboxylic acid derivatives with PO-containing groups (DE10242106A1).
For example, in the product Adhese (Ivoclar Vivadent) a hydrolysis-stable phosphonic acid ether acrylate is added as an acidic component.
In the use of self-etching dental adhesives the steps of conditioning and subsequent application of the adhesive (bonding) are combined into one step. A previous, separate etching of the hard substances of the tooth (enamel, dentin) with phosphoric acid is omitted. In the case of the dentin the acid-containing adhesive systems dissolve the smear layer and expose the underlying dentin or make the smear layer penetrable for the adhesive. Simultaneously to this, the infiltration of the monomers into the hard substances of the tooth takes place. In the case of the enamel an etching pattern similar to that of phosphoric acid etching is produced by the acid-containing adhesive system. Subsequently, the solvent necessary for the etching process and for infiltration is removed with an air cushion and the adhesive hardened by irradiation.
Self-conditioning adhesives contain as active component acidic monomers capable of polymerization. As a rule these monomers are (meth)acrylic acid esters of organic or inorganic acids. As examples of acidic monomers let phosphoric acid esters, such as HEMA phosphate, or esters of trimellitic acid or trimellitic acid anhydride be named.
From organic chemistry it is known that esters in acidic, aqueous solution are not hydrolysis-stable. Accordingly, hydrolytic cleavage can occur during storage of said acidic monomers in aqueous solutions within a few weeks to months. Thus it can be shown that in the hydrolysis of HEMA phosphate the compounds methacrylic acid, HEMA, and phosphoric acid are released. The rate of hydrolysis is, among other things, dependent on the pH value temperature and runs clearly more slowly in cold storage.
The objective is presented of providing hydrolysis-stable monomers which are suitable for the production of self-conditioning adhesives.